The usual electronics distributors: Mouser, Digikey, Newark (Farnell) all have them in their online catalogs, but they are mostly "out of stock." Newark claims to have 24: http://www.newark.com/atmel/atsam3x8ea-au/qfp144-green-ind-temp-mrla/dp/92T0815I don't know about international distributors...It looks like the chip is not quite in "full production" yet, which is a bit scary given Atmel's track record.

Since that appears to be designed for the STM32F chips, it may not work with the Atmel chips.

The particular ARM chip used on Due has lots of features (Ethernet, USB Host/Device, CAN controller, 512k flash, multi-channel DMA) and isn't likely to ever compete with the very low cost ARM chips being sold by other vendors. You can get some of the smaller SAM3x chips for less, and some of the lesser SAM3 chips are very cheap, and they'd be at least THEORETICALLY compatible with the new Arduino IDE.

Also, it looks the the prices drop pretty quickly in larger quantities (~30% at 25 for one I looked at...)